Airplanes are fun to work on for plane nuts. Not for car freaks, I've seen dozens of car mechanics enter the profression thinking they'd make more money only to leave after a few years, easily finding a better paying, better hours job in the automotive world. Pay will always be poor for aircraft mechanics, for a number of reasons, number one we're mechanics, as far as aviation is concerned, theres not much below us maybe rampers, remember, in the military the pilots are the officers, the mechanics are enlisted this is where it all starts. Airlines will always have good times and bad times, but more bad then good even when pay starts to pick up, it seems bankruptcies aren't far behind. In the automotive industry labor is charged hourly to the customer (in many cases, not all), if an airline were to increase your hourly wage, they would have no way to directly bill it to the customer. (they could increase ticket prices, but we all know how this works in reality). Aircraft mechanics are aircraft mechanics often for a reason, its kind of like going to the car dealership and telling the salesman, how the car he's showing you is just what you want, and how excited you are to buy it, you're not gonna get a good deal, "real"(that is the real plane nuts out there) aircraft mechanics are probably not going to leave the industry unless completely forced out. So what incentive do the airlines have to pay you more to keep you around, if their only competition is a rival airline who's probably not hiring and will start you at senority zero, not much. Another major downer to the industry, is mechanics can only work on the airplanes when they're not flying, that means almost all of the work is done at night and on weekends, when the planes aren't in the air. I've worked almost 4 years now, weekends and graveyard shift, and have no prospect in my seniority list(400+) of achieving weekends off in the next 3 years. It may sound like I'm whining, but I have my job, and I plan on keeping it, but I've wanted to work on airplanes since I was 5, this is my dream. No job may be perfect, but I'd just like to save your friend, some grief and heartache. If he's not willing to sacrifice and put his all into an aviation job then tell him not to bother, honestly the industry doesn't need to pay for training of another auto mechanic who can do better.
Hope my response helps him make a decision, sorry if its slightly incoherent, I've just gotten off of work this morning. I'm sure theres plenty more other a&P's can add to my list. Maybe a GA
mechanic on here could give some insight into that side of the field, but from the people I know working in it, its not much better.